1. Field of the Invention
The present invention relates to a semiconductor device and a method of selecting the same and, more particularly, to a semiconductor device having a PHS (Plated Heat Sink) structure and a method of selecting specific kind of chips from a semiconductor substrate with the PHS structure including several kinds of chips.
2. Description of the Prior Art
Conventionally, in manufacturing a high-output semiconductor device having a PHS structure, product chips (a chip having a practical signal processing function is called a product chip so as to be distinguished from a TEG chip to be described later upon completion of a semiconductor device) obtained by dividing a wafer into chips selected using tweezers or the like. This method, however, has bad workability, and requires a large number of steps. Particularly, when one wafer includes several kinds of product chips and TEG (Test Element Group, i.e., an evaluation element group for checking the element characteristics of, e.g., a transistor in a wafer) chips, selection by outer appearances must be performed using a microscope or the like to distinguish specific product chips from others, undesirably increasing the number of selection steps.
In order to solve the above problem and decrease the number of selection steps, a method of sticking a ferromagnetic adhesive tape on unnecessary chips, and a method of coating a ferromagnetic ink on unnecessary chips, and magnetically selecting and removing the coated chips are available (e.g., see Japanese Unexamined Patent Publication Nos. 59-88843 and 59-215739). FIGS. 1A and 1B show these selection methods described in these prior arts. FIG. 1A shows a state wherein a ferromagnetic adhesive tape 52 is stuck on the surface of a semiconductor chip 51 as a rejection mark, and FIG. 1B shows a selection state. Referring to FIG. 1B, an acceptable semiconductor chip 53 and a rejected semiconductor chip 54 are conveyed on a belt 55, and a magnet 56 selects and removes only the rejected semiconductor chip 54.
By using the above selection method, an unnecessary chip can be easily, effectively removed. However, when one wafer includes several kinds of product chips, and only a specific kind of chips are to be selected from these chips at a non-defective product level without damage, the magnetic tape cannot be stuck on the surfaces of the chips, or the magnetic ink cannot be coated thereon, as a matter of course. Although a method of attaching these materials on the lower surfaces of the chips can be considered, the magnetic material causes a circuit operation error on chips using transistors such as GaAs FET. Therefore, this method cannot be properly applied to product chips.